Toscafund joins Dutch bank SNS, Dutch pension provider PGGM and another British hedge fund The Children's Institution (TCI) in calling for a shake-up of AM strategy after disappointing returns for its investors.
Although ABN's market capitalisation of $67 billion makes it the Netherlands' biggest bank, latterly its share price has stagnated.
Speaking in a statement, Toscafund, said: "It is evident that over the past five years the management of ABN Amro has failed to deliver acceptable returns.
"Accordingly, we do not believe that ABN Amro should make any major acquisitions. We also believe that all the stakeholders would benefit by way of a merger with another large group which has a proven track record in adding value."
TCI, SNS AND Toscafund hold stakes of one per cent, 0.23 per cent, one per cent respectively. PGGM'S stake is undisclosed.